When human knee is viewed from a modelling standpoint, the lower limb motion is essentially a rocking motion. This report documents the details of selection, synthesis and analysis of the mechanism. In particular, a slider crank mechanism is selected to imitate the dominant motion of knee joint, extension and flexion. A CAD model of the knee exoskeleton is developed later which incorporated the housing for lead screw, DC motor, microcontroller and the motor driver. An accelerometer is placed on the chest of a child to record the gait cycle. The commands are sent to the DC motor according to the values of accelerometer via microcontroller. Belt and pulleys help to transmit the required power of DC motor into the lead screw of the mechanism, to translate the lead screw. Implemented the PID control on hardware setup to control knee exoskeleton according to target function, to recover the knee joint motion with this 1-DOF knee exoskeleton.